Allow non-image mime-types in the multiple featured image plugin

MFI_more_mime_types.php

// In function kd_meta_box_output() replace

$thumbnail = wp_get_attachment_image( $image_id, array( 266, 266 ) );

//With...
$type = get_post_mime_type($iamge_id);
$icon = in_array($type, array('application/pdf')) ? true : false;
                
$thumbnail = wp_get_attachment_image( $image_id, array( 266, 266 ), $icon );


// And in function kd_ajax_set_image(), replace
$thumb_html = wp_get_attachment_image( $thumb_id, 'thumbnail', $icon);

//With...
$type = get_post_mime_type($thumb_id);
$icon = in_array($type, array('application/pdf'))? true : false;
   
$thumb_html = wp_get_attachment_image( $thumb_id, 'thumbnail', $icon);